U.S. Pat No. 5,780,565 (Clough et al.) describe mixtures of liquid or supercritical CO.sub.2 and either perfluorocarbons or hydrofluorocarbons as a polymerization media in which the polymers produced are insoluble in the media.
U.S. Pat. No. 5,515,920 (Luk et al.) describes the use of a mixture of a liquified gas, such as CO.sub.2, and particulate proppants as a fracturing fluid for stimulating the production of crude oil and natural gas from wells in reservoirs of low permeability.
Published patent application WO 96/27704 described a system for dry cleaning comprising "densified" CO.sub.2 and a surfactant. The surfactant comprising "CO.sub.2 -philic" and "CO.sub.2 -phobic" moieties. Published patent application WO 97/16264 describes a system for dry cleaning comprising fluid CO.sub.2 and functional fluorinated compounds.
Mixtures of nitrogen and carbon dioxide are known in the art. Arai et al. have reported the pressure, volume, temperature and compositional relationships for the binary system in Journal of Chemical Engineering of Japan, volume 4, no. 2, 1971, pp. 113-122.
U.S. Pat No. 4561452 (Gahrs) describes the use of compressed gaseous solvents comprising mixtures of carbon dioxide and nitrogen to extract nicotine from tobacco and U.S. Pat No. 4,714,617 (Gahrs) describes the use of of compressed gaseous solvents comprising mixtures of carbon dioxide and nitrogen to extract caffeine from coffee.
However, even under high shear conditions, emulsions or foams of liquid CO.sub.2 and nitrogen are generally not stable, and readily phase separate leading to fluid and/or gas losses as well as changes in the rheological properties of the fluid. Accordingly, it would be desirable to stabilize such compositions.